Norfolk Police gave brief details of their initial findings following yesterday’s incident which blocked the main road until late evening.

Inspector Chris Brooks said: “We’ve already interviewed some of the passengers on board as well as drivers who were in the area at the time of the incident.

“As a result of initial inquiries we know just prior to the incident that people were queuing for the toilet. Somehow, the door has opened and the boy has fallen from the moving coach.”

The 71-seater double decker coach has now been taken to a secure compound for further investigation.

The incident happened shortly before 3.45pm as the group of 30 passengers, 20 children and 10 adults, travelled home to Lincolnshire after the youngsters, from Stamford Rugby Club, had played in a tournament at Holt in north Norfolk.

The boy remains in a critical condition in Addenbrooke’s Hospital in Cambridge - his father was travelling on the 71-seater double-decker coach while his mother was travelling in a car as part of the convoy.

The boy has been named locally as Sebastian Goold who was described today by club officials as a “promising” player. The club chairman Neil Jolly met a replacement coach with parents and players on board when it arrived back in the town last night. Earlier the passengers had been taken to a rest centre at Kings Lynn police station to await the alternative transport.

Mr Jolly said the thoughts of everyone at the club were with Sebastian and his family.

Inspector Brooks said: “This is a very difficult time for the boy’s family and we have specially trained officers supporting them.

“The coach was recovered yesterday and is being kept in a secure compound. The vehicle will be examined by police and VOSA investigators and this is the focus of our enquiry at this stage.

“We will also be speaking to other people who were on board at the time of the incident and it would be inappropriate to speculate on possible causes at this stage.”

Anyone who witnessed the incident is asked to contact the Serious Collision Investigation Team at Norfolk Police on 101.